The present invention relates to an image forming apparatus in which an electrophotographic technique and the like are utilized to transfer image information onto a transfer material and to form an image, particularly to driving connection of the image forming apparatus.
In a conventional image forming apparatus in which an electrophotographic technique has heretofore been employed, an electrophotographic photoconductor served as an image carrier is charged by a charging unit, and irradiated with light corresponding to the image information, to form a latent image thereon. A toner image formed by developing the latent image by a developing unit is transferred to a sheet material and the like so that the image is formed.
In such an image forming apparatus, there is a technical problem as to minimizing an image jitter, density unevenness and transfer position deviation. Examples of factors which determines such properties include a speed fluctuation of the photoconductor, and it is very important to develop a driving unit having little speed fluctuation.
A driving system of a conventional image forming apparatus will be described hereinafter with reference to FIGS. 26 and 27. FIG. 26 is a perspective view showing a driving unit and a photoconductor drum of the conventional image forming apparatus, and FIG. 27 is an explanatory view showing an engagement state of a driving spline and a follower spline of FIG. 26.
In FIG. 26, a driving unit 2 has involute spline shafts (driving splines) 18 for transmitting a rotation force to photoconductor drums (photoconductors) 1a to 1d as image carriers. The involute spline shaft 18 is rotated by a driving motor (not shown) via a reduction mechanism (not shown). The rotation force of the spline shaft is transmitted to each of involute spline holes (follower spline) 19 mounted on rotation shafts of the photoconductor drums 1a to 1d, so that the photoconductor drums 1a to 1d are rotated.
However, there is looseness in the spline engagement between the involute spline shaft 18 and the involute spline hole 19. Particularly, with respect to the looseness of a peripheral direction, the photoconductor drums 1a to 1d are moved by the looseness when a load fluctuates. This generates an image jitter, density unevenness, and transfer position deviation.
In actual, various mechanisms are necessary for forming the images in peripheries of the photoconductor drums 1a to 1d. Examples of such the mechanisms include developing means (not shown) for developing electrostatic latent images formed on the photoconductor drums 1a to 1d, transfer means (not shown) for transferring the toner images developed on the photoconductor drums 1a to 1d to a transfer material, and the like. Rotations of the photoconductor drums 1a to 1d are influenced by rotation and load fluctuations of these mechanisms, and the drums are easily moved.
To solve the problem, as shown in FIG. 26, torque limitters 21a, 21b, 21c, 21d are attached as load means to the photoconductor drums 1a to 1d. The looseness of the peripheral direction in the spline engagement between the involute spline shaft 18 and the involute spline hole 19 is constantly removed in one direction, that is, a rotation direction P as shown in FIG. 27, so that the photoconductor drums 1a to 1d steadily rotate.
However, of the photoconductor drum requires the load means such as the torque limitters 21a, 21b, 21c, 21d for constantly displacing the engagement looseness in the peripheral direction of the spline in one direction. Therefore, in the aforementioned conventional driving technique, there is a first problem that a driving force increases, the driving unit is enlarged, and cost-up is caused.
Particularly, in a multi-image forming apparatus of a tandem system including a plurality of photoconductor drums, and the like, since the number of load means corresponding to the number of photoconductor drums are necessary, the driving force largely increases, and the problem becomes very large.
Moreover, the influence of the engagement looseness in the peripheral direction is reduced or canceled by the load means such as the torque limitter, but the looseness in a radius direction remains. Due to the looseness, rotation centers of the follower spline and a driving spline deviate, the rotation of the driving spline is not exactly transmitted to the follower spline, and the rotation fluctuation of the photoconductor drum is caused. Thus, there is a second problem that the image jitter, density unevenness, and transfer position deviation are generated.
Particularly, in the multi-image forming apparatus of the tandem system including the plurality of photoconductor drums, since the transfer position deviation results in color deviation, the problem becomes very serious.
Moreover, for color images, a large number of image forming apparatuses of the tandem system have heretofore been proposed in which a plurality of image carriers with the aforementioned series of image forming process developed therein is included, and respective color images such as cyan, magenta, and yellow images, and preferably a black image are formed on the respective image carriers, and are superposed and transferred onto a sheet material in transfer positions of the respective image carriers, to form a full-color image. The multi-image forming apparatus of the tandem system is said to be advantageous for a high speed because respective image forming sections are disposed for the respective colors.
For example, as described in specifications proposed by the present applicant and filed as JP-A-2000-284592, the multi-image forming apparatus of the tandem system includes: image forming units for forming toner images of respective colors such as yellow (Y), magenta (M), cyan (C), and black (K); an exposure unit for outputting an image signal and forming an electrostatic latent image; an intermediate transfer belt formed and run in a closed loop shape; and a fixing unit. The toner images on the intermediate transfer belt are transferred onto the sheet material supplied from a sheet cassette and fixed onto the sheet material by the fixing unit.
Since the respective image forming units of yellow (Y), magenta (M), cyan (C), and black (K) have a common structure, one of the image forming units is shown in FIG. 28.
As shown in FIG. 28, the image forming unit is a combination of: a photoconductor unit including a photoconductor drum 102 having a peripheral surface with an electrostatic latent image formed thereon by a laser beam 109d of an exposure unit 106d, charging means 134 for charging the photoconductor drum 102, and cleaning means 126 for removing a residual toner from the surface of the photoconductor drum 102; and a developing unit including a toner supply roller 122 for supplying toner to a developing roller 121 which contacts the photoconductor drum 102, and a layer thinning blade 123, disposed in contact with the developing roller 121, for uniformly thinning a toner layer and charging the toner layer at a predetermined potential.
In the image forming unit, the electrostatic latent image of image information is formed on the photoconductor drum 102 by the exposure unit 106d. The electrostatic latent image is visualized as the toner image by the developing roller 121, and transferred onto the intermediate transfer belt. Moreover, in the four-colors image forming apparatus, the respective color toner images are transferred onto the intermediate transfer belt and the multi-color image is finally formed.
A conventional technique will be described hereinafter with reference to the drawings.
FIGS. 29 to 33 are perspective views showing a part of the conventional image forming apparatus in detail.
As shown in FIG. 29, for driving transmission of the photoconductor drum 102 in the conventional image forming apparatus, a gear driving system is used in many cases. In the system, a gear is formed on a driving-side flange 129d press-fitted coaxially with a rotation shaft of the photoconductor drum 102 in one end of the photoconductor drum 102, and further a driving pulley 128a which meshes with the gear is disposed. The driving force is transmitted by one or a plurality of driving motors disposed on a driving side of the apparatus via the driving pulley 128a. 
When driving is transmitted by the gears in this manner, there is a problem that a counterforce by which the gears tries to be detached from each other is generated, and thus, the photoconductor drum 102 vibrates, a writing position of the electrostatic latent image onto the photoconductor drum 102 fluctuates, and the deviation is generated in the image.
In recent years, to solve the problem, as shown in FIG. 30, an involute spline driving system has been used, in which an internal involute spline is formed on an inner peripheral surface of a driving-side flange 129c press-fitted coaxially with the rotation shaft of the photoconductor drum 102 in the end of the photoconductor drum 102, and an external involute spline is formed correspondingly to the internal involute spline in a driving pulley 128 disposed coaxially with the photoconductor drum 102, so that the driving is transmitted at a high precision.
In the involute spline driving system, the driving force supplied by one or a plurality of driving motors disposed on the driving side of the apparatus is transmitted to the driving-side flange 129c press-fitted in the photoconductor drum 102 via the driving pulley 128. Moreover, with respect to the driving transmission to other members to be driven, as shown in FIG. 31, the driving force is transmitted to a developing roller gear 131b fixed to the developing roller 121 from the gear formed on a non-driving side flange 130b press-fitted in the photoconductor drum 102. Moreover, as shown in FIG. 32, the force is transmitted to a charging means gear 132b fixed to the charging means 134. Furthermore, as shown in FIG. 33, the force is transmitted to a disposal toner carrying screw gear 133b fixed to a disposal toner carrying screw 127.
According to the constitution, a gear needs to be formed on a non-driving side flange, and thus, high cost results.
Moreover, since the gear for transmitting the driving force needs to be disposed also on the non-driving side, a large space is necessary.
As described above, in the conventional image forming apparatus, there is a third problem of a high cost and large space in distributing the driving force transmitted to the photoconductor drum.
In the first problem as mentioned above, an object of the present invention is to provide an image forming apparatus which can cancel looseness of a peripheral direction of a driving spline and a follower spline without using any load means.
In the second problem, an object of the present invention is to provide an image forming apparatus which can cancel looseness of a radius direction of the driving spline and the follower spline without using any load means.
In order to solve the first and second problems, according to a first aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier; a driving unit for transmitting a driving force to the image carrier via a driving spline; and a plurality of members to be driven for receiving the driving force transmitted from the driving unit via the image carrier. The image forming apparatus further comprises a follower spline attached onto a rotation shaft of the image carrier. The follower spline is positioned and connected to the driving spline so that the follower spline contacts the driving spline by tooth surfaces on opposite sides and gaps are formed between a tooth tip and a tooth root of the follower spline and the driving spline. The driving force of the driving unit transmitted from the driving spline is transmitted to the photoconductor so that the photoconductor is rotated.
Moreover, in order to solve the first and second problems, according to a second aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier; a driving unit for transmitting a driving force to the image carrier via a driving spline; and a plurality of members to be driven for receiving the driving force transmitted from the driving unit via the image carrier. The image forming apparatus further comprises a follower spline attached onto a rotation shaft of the image carrier. The follower spline is positioned and connected to the driving spline so that the follower spline contacts the driving spline by tooth surfaces on opposite sides, a root portion of the follower spline also contacts a tooth tip of the driving spline, and a gap is formed between the tooth tip of the follower spline and the driving spline. The driving force of the driving unit transmitted from the driving spline is transmitted to the image carrier so that the image carrier is rotated.
With these constitutions, since the looseness in the peripheral direction of the driving spline and the follower spline can be canceled, the load means such as a torque limitter is abolished, a driving load can be reduced, and miniaturization of an image carrier driving system and cost reduction can be achieved.
Moreover, since the looseness in the radius direction can be also canceled, and a rotation center of the driving spline is allowed to coincide with a rotation center of the follower spline with good precision, an angular speed fluctuation is reduced or canceled. Thus, it is possible to reduce or cancel jitter, density unevenness, and transfer position deviation of an AC component at a low cost under a simple structure.
Furthermore, in the first and second aspects, a diameter of the tooth tip in the driving spline at a tip end side in a rotation axial direction, i.e. at the follower spline side, may be set to be smaller than that at the root portion in the rotation axial direction, i.e. at the driving unit side. A tooth width in the driving spline at the tip end in the rotation axial direction, i.e. at the follower spline side, may be set to be smaller than that at the root portion in the rotation axial direction, i.e. at the driving unit side. Thus, a step may be disposed in this manner. Additionally, the diameter of the tooth tip or the tooth width in the driving spline may be gradually reduced toward the tip end from the root portion or a middle portion between the root portion and the tip end in the rotation axial direction of the driving spline so that a taper may be made.
Furthermore, a tooth shape of an involute spline as the force receiving means could be replaced for various tooth shapes of spline; i.e., a round tooth shape spline, a rectangle tooth shape one or the like.
Moreover, in order to solve the above-mentioned third problem, according to a third aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier; a driving unit for transmitting a driving force to the image carrier; and a flange disposed coaxially with a rotation shaft of the image carrier in one end of the image carrier. A driving force receiving means to which the driving force is transmitted from the driving unit is formed on an inner peripheral surface of the flange, and driving force transmission means for transmitting the driving force to at least one of a plurality of members to be driven for receiving the driving force transmitted from the driving unit via the flange is formed on an outer peripheral surface of the flange.
Furthermore, in order to solve the above-mentioned third problem, according to a fourth aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier; a driving unit for transmitting a driving force to the image carrier; and a flange disposed coaxially with a rotation shaft of the image carrier in one end of the image carrier. An involute spline shape to which the driving force is transmitted from the driving unit is formed on an inner peripheral surface of the flange, and driving force transmission means for transmitting the driving force to at least one of a plurality of members to be driven for receiving the driving force transmitted from the driving unit via the flange is formed on an outer peripheral surface of the flange.
With the constitutions, it is unnecessary to form the driving force transmission means in a flange on a driven side. While low cost is realized, it is possible to transmit the driving force to another member or other members to be driven at high precision.
Moreover, since the gears are concentrated only on the driving side, space saving is achieved, and it is also possible to transmit the driving force to another member to be driven at high precision.
Furthermore, in the third and fourth aspects, the image carrier may be a photoconductor drum, and the member to be driven may be a developing roller, charging means, or disposal toner screw.
Moreover, in order to solve the above-mentioned first, second, and third problems, according to a fifth aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier; a driving unit for transmitting a driving force to the image carrier via a driving spline; and a plurality of members to be driven for receiving the driving force transmitted from the driving unit via the image carrier. The image forming apparatus further comprises a driving-side flange disposed coaxially with a rotation shaft of the image carrier in one end of the image carrier. A follower spline having an involute spline shape to which the driving force is transmitted from the driving unit via a driving spline is formed on an inner peripheral surface of the driving-side flange, and driving force transmission means having a predetermined gear shape for transmitting the driving force to at least one of the members to be driven is formed on an outer peripheral surface of the flange. Furthermore, the follower spline of the driving-side flange attached onto the rotation shaft of the image carrier is positioned and connected to the driving spline so that the follower spline contacts the driving spline by tooth surfaces on opposite sides and gaps are formed between a tooth tip and a tooth root of the follower spline and the driving spline. The driving force of the driving unit transmitted from the driving spline is transmitted to the image carrier so that the image carrier is rotated.
Moreover, to solve the first, second, and third problems, according to a sixth aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier; a driving unit for transmitting a driving force to the image carrier via a driving spline; and a plurality of members to be driven for receiving the driving force transmitted from the driving unit via the image carrier. The image forming apparatus further comprises a driving-side flange disposed coaxially with a rotation shaft of the image carrier in one end of the image carrier. A follower spline having an involute spline shape to which the driving force is transmitted from the driving unit via the driving spline is formed on an inner peripheral surface of the driving-side flange, and driving force transmission means having a predetermined gear shape for transmitting the driving force to at least one of the members to be driven is formed on an outer peripheral surface of the flange. Moreover, the follower spline of the driving-side flange attached to the rotation shaft of the image carrier is positioned and connected to the driving spline so that the follower spline contacts the driving spline by tooth surfaces on opposite sides, a root portion of the follower spline also contacts a tooth tip of the driving spline, and a gap is formed between the tooth tip of the follower spline and the driving spline. The driving force of the driving unit transmitted from the driving spline is transmitted to the image carrier so that the image carrier is rotated.
According to these constitutions, since the looseness in the peripheral direction of the driving spline and the follower spline can be canceled, the load means such as a torque limitter is abolished, a driving load can be reduced, and miniaturization of an image carrier driving system and cost reduction can be achieved. Moreover, since the looseness in the radius direction can also be canceled, and a rotation center of the driving spline is allowed to coincide with a rotation center of the follower spline with good precision, an angular speed fluctuation is reduced or canceled. Thus, it is possible to reduce or cancel jitter, density unevenness, and transfer position deviation of an AC component at a low cost under a simple structure. Furthermore, it is unnecessary to form the driving force transmission means in a flange on a driven side. While low cost is realized, it is possible to transmit the driving force to another member or other members to be driven at high precision.